Targeting protein translation in human non small cell lung cancer via combined MEK and mammalian target of rapamycin suppression

Lung cancer is a genetically heterogeneous disease characterized by the acquisition of somatic mutations in numerous protein kinases, including components of the rat sarcoma viral oncogene homolog (RAS) and AKT signaling cascades. These pathways intersect at various points, rendering this network highly redundant and suggesting that combined mitogen-activated protein/extracellular signal-regulated kinase (MEK) and mammalian target of rapamycin (mTOR) inhibition may be a promising drug combination that can overcome its intrinsic plasticity. The MEK inhibitors, CI-1040 or PD0325901, in combination with the mTOR inhibitor, rapamycin, or its analogue AP23573, exhibited dose-dependent synergism in human lung cancer cell lines that was associated with suppression of proliferation rather than enhancement of cell death. Concurrent suppression of MEK and mTOR inhibited ribosomal biogenesis by 40% within 24 h and was associated with a decreased polysome/monosome ratio that is indicative of reduced protein translation efficiency. Furthermore, the combination of PD0325901 and rapamycin was significantly superior to either drug alone or PD0325901 at the maximum tolerated dose in nude mice bearing human lung tumor xenografts or heterotransplants. Except for a PTEN mutant, all tumor models had sustained tumor regressions and minimal toxicity. These data (a) provide evidence that both pathways converge on factors that regulate translation initiation and (b) support therapeutic strategies in lung cancer that simultaneously suppress the RAS and AKT signaling network.

Enhancement of the therapeutic efficacy of taxol by the mitogen-activated protein kinase kinase inhibitor CI-1040 in nude mice bearing human heterotransplants

Taxol may contribute to intrinsic chemoresistance by activating the mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) cytoprotective pathway in human cancer cell lines and tumors. We have previously shown additivity between Taxol and the MEK inhibitor, U0126 in human cancer cell lines. Here, the combination of Taxol with an orally bioavailable MEK inhibitor, CI-1040, was evaluated in human lung tumors heterotransplanted into nude mice. Unlike xenograft models that are derived from cells with multiple genetic alterations due to prolonged passage, heterotransplanted tumor models are more clinically relevant. Combined treatment with both drugs resulted in inhibition of tumor growth in all models and tumor regressions in three of four models tested, supporting our previous observation that Taxol's efficacy is potentiated by MEK inhibition. Concurrent administration was superior to intermittent dosing. Pharmacodynamic assessments of tumors indicated that suppression of MEK was associated with induction of S473 phosphorylated Akt and reduced proliferation in the combination groups relative to single agents, in addition to suppression of fibroblast growth factor-mediated angiogenesis and reduced expression of vascular endothelial growth factor. These findings are significant and indicate that this combination may have broad therapeutic applications in a diverse range of lung tumors with different intrinsic chemosensitivities.

Potentiation of taxol efficacy and by discodermolide in ovarian carcinoma xenograft-bearing mice

PURPOSE

To evaluate the drug combination of discodermolide and Taxol in human ovarian cancer cells and in an in vivo model of ovarian carcinoma.

EXPERIMENTAL DESIGN

The combination index method was used to evaluate the interaction of Taxol and discodermolide in human ovarian SKOV-3 carcinoma cells. Data were correlated with alterations in cell cycle distribution and caspase activation. In addition, SKOV-3 xenograft-bearing mice were treated with either Taxol, discodermolide, or a combination of both drugs given concurrently to evaluate the antitumor efficacy and toxicity of this combination. The Matrigel plug assay and CD31 immunohistochemistry were done to assess antiangiogenic effects.

RESULTS

Taxol and discodermolide interact synergistically over a range of concentrations and molar ratios that cause drug-induced aneuploidy in ovarian carcinoma cells. In SKOV-3 xenograft-bearing mice, the combination is significantly superior to either single agent, and induces tumor regressions without notable toxicities. Immunohistochemical analysis of CD31 and Matrigel plug analysis show decreased vessel formation in mice treated with the combination relative to either drug alone.

CONCLUSIONS

The synergistic activity of Taxol and discodermolide in cells is most potent at drug concentrations that result in drug-induced aneuploidy rather than mitotic arrest. Moreover, in an animal model of ovarian carcinoma, this is a well-tolerated combination that induces tumor regressions and suppresses angiogenesis. These data confirm the potency of this combination and support the use of concurrent low doses of Taxol and discodermolide for potential use in cancer therapeutics.

P450 inhibitor ketoconazole increased the intratumor drug levels and antitumor activity of fenretinide in human neuroblastoma xenograft models

We previously reported that concurrent ketoconazole, an oral anti-fungal agent and P450 enzyme inhibitor, increased plasma levels of the cytotoxic retinoid, fenretinide (4-HPR) in mice. We have now determined the effects of concurrent ketoconazole on 4-HPR cytotoxic dose-response in four neuroblastoma (NB) cell lines in vitro and on 4-HPR activity against two cell line-derived, subcutaneous NB xenografts (CDX) and three patient-derived NB xenografts (PDX). Cytotoxicity in vitro was assessed by DIMSCAN assay. Xenografted animals were treated with 4-HPR/LXS (240 mg/kg/day) + ketoconazole (38 mg/kg/day) in divided oral doses in cycles of five continuous days a week. In one model, intratumoral levels of 4-HPR and metabolites were assessed by HPLC assay, and in two models intratumoral apoptosis was assessed by TUNEL assay, on Day 5 of the first cycle. Antitumor activity was assessed by Kaplan-Meier event-free survival (EFS). The in vitro cytotoxicity of 4-HPR was not affected by ketoconazole (p ≥ 0.06). Ketoconazole increased intratumoral levels of 4-HPR (p = 0.02), of the active 4-oxo-4-HPR metabolite (p = 0.04), and intratumoral apoptosis (p ≤ 0.0006), compared to 4-HPR/LXS-alone. Concurrent ketoconazole increased EFS in both CDX models compared to 4-HPR/LXS-alone (p ≤ 0.008). 4-HPR + ketoconazole also increased EFS in PDX models compared to controls (p ≤ 0.03). Thus, concurrent ketoconazole decreased 4-HPR metabolism with resultant increases of plasma and intratumoral drug levels and antitumor effects in neuroblastoma murine xenografts. These results support the clinical testing of concurrent ketoconazole and oral fenretinide in neuroblastoma.

Complex effects of Ras proto-oncogenes in tumorigenesis

Ras proteins have been found mutated in about one-third of human tumors. In vitro, Ras has been shown to regulate distinct and contradictory effects, such as cellular proliferation and apoptosis. Nonetheless, the effects that the wild-type protein elicits in tumorigenesis are poorly understood. Depending on the type of tissue, Ras proto-oncogenes appear to either promote or inhibit the tumor phenotype. In this report, we treated wild-type and N-ras knockout mice with 3-methylcholanthrene (MCA) to induce fibrosarcomas and found that MCA is more carcinogenic in wild-type mice than in knockout mice. After injecting different doses of a tumorigenic cell line, the wild-type mice exhibited a shorter latency of tumor development than the knockouts, indicating that there are N-ras-dependent differences in the stromal cells. Likewise, we have analyzed B-cell lymphomas induced by either N-methylnitrosourea or by the N-ras oncogene in mice that over-express the N-ras proto-oncogene and found that the over-expression of wild-type N-ras is able to increase the incidence of these lymphomas. Considered together, our results indicate that Ras proto-oncogenes can enhance or inhibit the malignant phenotype in vivo in different systems.

Combined MEK and mTOR suppression is synergistic in human NSCLC and is mediated via inhibition of protein translation

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Background: Lung cancer is a heterogeneous disease characterized by the acquisition of somatic mutations in numerous protein kinases, including components of RAS and AKT. These intersect at various points rendering the network highly redundant. Hence, dual suppression of both, using MEK and mTOR inhibitors may be a promising rational drug combination that can overcome the intrinsic plasticity of this signaling network. Methods: The concurrent combination of the MEK inhibitor CI-1040 and the mTOR inhibitor AP23573 was evaluated in non-small cell lung cancer (NSCLC) cell lines, using the combination index method of Chou and Talalay. The concurrent combination of Rapamycin and the MEK inhibitor PD0325901 was also evaluated in animal models of human lung cancer. Results: The MEK inhibitors, CI-1040 or PD0325901, in combination with the mTOR inhibitor rapamycin, or its analog AP23573, were synergistic in human lung cancer cell lines. Statistically significant enhancement of cell death by the combination of MEK and mTOR inhibitors was not observed. Rather, synergism was associated with suppression of proliferation and inhibition of protein translation. Concurrent suppression of both MEK and mTOR inhibited ribosomal biogenesis by forty percent after twenty-four hours and was associated with a block in the initiation phase of translation. Furthermore, the combination of PD0325901 and rapamycin was significantly superior to either drug alone, or PD0325901 at the maximum tolerated dose, in xenograft and human heterotransplanted lung tumor models grown in nude mice. Conclusions: These data support therapeutic strategies in lung cancer that simultaneously suppress RAS and mTOR signaling networks, and provide evidence that both pathways converge on factors that regulate protein translation initiation.

No significant financial relationships to disclose.

The O6-methyguanine-DNA methyltransferase inhibitor O6-benzylguanine enhanced activity of temozolomide + irinotecan against models of high-risk neuroblastoma

DNA-damaging chemotherapy is a major component of therapy for high-risk neuroblastoma, and patients often relapse with treatment-refractory disease. We hypothesized that DNA repair genes with increased expression in alkylating agent resistant models would provide therapeutic targets for enhancing chemotherapy. In-vitro cytotoxicity of alkylating agents for 12 patient-derived neuroblastoma cell lines was assayed using DIMSCAN, and mRNA expression of 57 DNA repair, three transporter, and two glutathione synthesis genes was assessed by TaqMan low-density array (TLDA) with further validation by qRT-PCR in 26 cell lines. O6-methylguanine-DNA methyltransferase (MGMT) mRNA was upregulated in cell lines with greater melphalan and temozolomide (TMZ) resistance. MGMT expression also correlated significantly with resistance to TMZ+irinotecan (IRN) (in-vitro as the SN38 active metabolite). Forced overexpression of MGMT (lentiviral transduction) in MGMT non-expressing cell lines significantly increased TMZ+SN38 resistance. The MGMT inhibitor O6-benzylguanine (O6BG) enhanced TMZ+SN38 in-vitro cytotoxicity, H2AX phosphorylation, caspase-3 cleavage, and apoptosis by terminal deoxynucleotidyl transferase dUTP nick end labeling. TMZ+IRN+O6BG delayed tumor growth and increased survival relative to TMZ+IRN in two of seven patient-derived xenografts established at time of death from progressive neuroblastoma. We demonstrated that high MGMT expression was associated with resistance to alkylating agents and TMZ+IRN in preclinical neuroblastoma models. The MGMT inhibitor O6BG enhanced the anticancer effect of TMZ+IRN in vitro and in vivo. These results support further preclinical studies exploring MGMT as a therapeutic target and biomarker of TMZ+IRN resistance in high-risk neuroblastoma.

Insights into the modular design of kinase inhibitors and application to Abl and Axl

Scaffold hopping is a common strategy for generating kinase inhibitors that bind to the DFG-out inactive conformation. Small structural differences in inhibitor scaffolds can have significant effects on potency and selectivity across the kinome, however, these effects are often not studied in detail. Herein, we outline a design strategy to generate an array of DFG-out conformation inhibitors with three different hinge-binders and two DFG-pocket groups. We studied inhibitor selectivity across a large segment of the kinome and elucidated binding preferences that can be used in scaffold hopping campaigns. Using these analyses, we identified two selective inhibitors that display low nanomolar potency against Axl or wild-type and clinically relevant mutants of Abl.

Abstract 2493: Enhanced activity of fenretinide/-LYM-X-SORBTM (4-HPR/LXS) oral powder in combination with ketoconazole and vincristine against recurrent neuroblastoma xenografts

Neuroblastoma (NB) is the most common extracranial solid tumor of childhood. Survival from relapsed NB is low and novel therapies are needed against recurrent NB, which often manifest loss of p53 function and multidrug resistance. Fenretinide (4-HPR) is a synthetic retinoid that achieved multiple complete responses in minimal disease in a phase I clinical trial in recurrent neuroblastoma when formulated as an oral powder using the LYM-X-SORBTM (LXS) organized lipid matrix (4-HPR/LXS). We recently showed that ketoconazole (keto) increased 4-HPR plasma concentrations in mice by > 2-fold over 4-HPR alone (P<0.02) (Br J Pharmacol 163:1263-75, 2011). To explore the anti-neuroblastoma activity in vivo of 4-HPR/LXS given with keto, we tested three human neuroblastoma xenografts established from patients with progressive disease, CHLA-119 and CHLA-90 (both TP53-mutant, multidrug-resistant cell lines) and COG-N-415x (from a progressive disease patient). 4-HPR/LXS was dosed at 240 mg/kg/day, keto at 38 mg/kg/day (both by oral gavagex5d/wk). 4-HPR and metabolite (4-oxo-4-HPR and 4-MPR) tumor concentrations were determined 4 h after last treatment and were quantified by HPLC. In the CHLA-119 xenograft, keto increased the complete response (CR) rate of 4-HPR/LXS from 1/10 mice to 5/10 mice. Survival >350 days with 4-HPR/LXS alone was 10% compared to 50% of mice treated with 4-HPR/LXS+keto (P< 0.005). 4-HPR/LXS+keto increased 4-HPR and 4-oxo-4-HPR tumor concentrations by > 2-fold over 4-HPR alone (P<0.02) and (P<0.04) respectively. We then added intravenous (i.v.) vincristine (VCR) at 0.5 mg/kg given twice a week every other week to the 4-HPR/LXS+keto regimen. In CHLA-119 xenografts, VCR increased the CR rate to 5/10 mice compared to 3/8 with 4-HPR/LXS+keto and 1/10 with VCR alone. Mouse survival for >300 days with 4-HPR/LXS+keto+VCR was 50% vs 38% with 4-HPR/LXS+keto (P<0.01) and 10% for VCR alone (P<0.003). COG-N-415x and CHLA-90 xenografts failed to achieve responses to 4-HPR/LXS or in combination with keto. Addition of VCR to 4-HPR/LXS+keto achieved CR's in 2/9 COG-415x mice compared to 0/9 and 0/8 for 4-HPR/LXS+keto and VCR alone, respectively. Survival of COG-415x mice was >90 days with 4-HPR+keto+VCR for 2/9 mice (22%) vs 0% for the other treatments (P<0.001). In CHLA-90 xenografts, 4-HPR/LXS+keto+VCR achieved 1 CR and 1 stable disease compared to no responses with 4-HPR/LXS+keto or VCR alone. CHLA-90 xenograft mouse survival for >60 days with 4-HPR/LXS+keto+VCR was 2/5 (40%) vs 0% for VCR or 4-HPR/LXS+keto alone. Toxicity of the combination regimens in mice (assessed by body weight) was negligible. These data suggest that if an ongoing phase I study of 4-HPR/LXS+keto is well-tolerated that a subsequent clinical trial exploring that combination+VCR should be undertaken in patients with recurrent NB. Supported by CPRIT RP10072.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2493. doi:1538-7445.AM2012-2493

Abstract 1327: UM-9107: A selective wild-type and T315I Bcr-Abl inhibitor with in vivo activity against chronic myelogenous leukemia

Purpose: Long-term treatment of chronic myelogenous leukemia (CML) with the Bcr-Abl inhibitor imatinib, is initially successful but gives rise to several drug-resistant mutations. The most prevalent of these is the T315I ‘gatekeeper’ mutation that is sensitive to the second-line therapy, ponatinib. However, ponatinib causes serious vascular adverse events, including fatalities, in over 25% of patients, in part due to its target promiscuity. We have designed a novel Bcr-Abl inhibitor (UM-9107) that shows significant in vitro and in vivo anti-CML activity against wild-type and drug-resistant mutants, including the gatekeeper mutant. Furthermore, UM-9107 has excellent selectivity across the kinome and in vitro surrogate toxicity assessment models demonstrate a low likelihood of vascular adverse events as compared to ponatinib.

Experimental Design: We designed a series of compounds to specifically interact with a specific kinked conformation of the phosphate-binding loop of Abl. Since only a small proportion of kinases display this kinked conformation, we hypothesized that our compounds would be selective for Abl. We have analyzed the compound series biochemically and in vitro. The most potent compound, UM-9107, has been comprehensively characterized including: biochemical inhibition, cellular target engagement, kinome-wide profiling, in vitro cell proliferation, pharmacokinetic studies, and in vivo activity in xenograft models of CML.

Results: We demonstrate that UM-9107 potently inhibits all clinical mutants of Bcr-Abl, including the T315I gatekeeper mutant. UM-9107 shows robust activity against CML cell lines, comparable to ponatinib, with significantly fewer off-targets, as determined by kinome-wide profiling. Phenotypic profiling of UM-9107 in human primary cells shows low risk of vascular adverse events as indicated by specific biomarker readouts. UM-9107 demonstrates good oral bioavailability and in vivo activity in xenograft models of CML, with low toxicity.

Conclusions: The success of imatinib has been revolutionary and has led to an increase in the number of patients on long-term therapy. This inevitably gives rise to drug resistance through point mutations in the Bcr-Abl protein. Our results suggest that UM-9107 is a safe and efficacious preclinical candidate for the treatment of imatinib-resistant CML.

Citation Format: Sameer Phadke, Lluis Lopez-Barcons, Taylor K. Johnson, Eric J. Lachacz, Sofia D. Merajver, Matthew B. Soellner. UM-9107: A selective wild-type and T315I Bcr-Abl inhibitor with in vivo activity against chronic myelogenous leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1327.

The N-ras proto-oncogene can suppress the malignant phenotype in the presence or absence of its oncogene

ras proto-oncogenes have traditionally been associated with the regulation and promotion of cell growth. We have induced thymic lymphomas in N-ras(-/-) mice and in transgenic mice that overexpress wild-type N-ras and found that the lack of wild-type N-ras alleles favors the development of thymic lymphomas,whereas overexpression of wild-type N-ras protects against thymic lymphomagenesis in the presence or absence of its oncogene. To investigate the inhibitory role of wild-type N-ras in in vitro transformation, we introduced wild-type N-ras in N-ras-deficient tumor cells that lack ras activating mutations and found decreased growth in both low serum and soft agar. Taken together, our results indicate that wild-type N-ras has "tumor suppressor" activity, even in the absence of its oncogenic allele.

Exogenous expression of H-cadherin in CHO cells regulates contact inhibition of cell growth by inducing p21 expression

The impact of the cadherins in human cancers is becoming better understood. However, few studies have directly tested the hypothesis that H-cadherin, a tailless cadherin, is actually a tumor suppressor, and no published studies have addressed the question of how H-cadherin suppresses cellular transformation. We report here the influence that exogenous expression of H-cadherin imposes on growth, morphology, clonogenicity and tumorigenicity of Chinese hamster ovarian (CHO) cells. H-cadherin expression in CHO cells resulted in tighter adhesion of multicellular aggregates and reduced cell proliferation. In addition to enhancement of cell-cell adhesion, exogenous H-cadherin expression also inhibited cell proliferation and the ability to form colonies in soft agar. Furthermore, expression of H-cadherin in CHO cells led to complete suppression of subcutaneous tumor growth in nude mice. Seeding the H-cadherin expressing CHO cells on culture plates coated with recombinant H-cadherin amino-terminal fragments resulted in inhibition of cell proliferation that was accompanied by increased expression of the cdk inhibitor p21. These results support the role of H-cadherin as a tumor suppressor participating in contact inhibition of cell growth, possibly by inducing p21 expression.